Nikon F-Mount
Direct Answer
The Nikon F-Mount (introduced in 1959 with the legendary Nikon F SLR) is one of the most storied lens mounts in photographic history, maintaining a continuous 46.5 mm Flange Focal Distance and 44.0 mm throat diameter for over 60 years. Spanning non-AI manual lenses to modern electronic-diaphragm AF-S/AF-E glass, over 100 million F-mount lenses were produced.
Source: Nikon Corporation 100th Anniversary Technical Archives / CIPA
Specs
| Flange Focal Distance (FFD) | 46.50 mm (1.831 in — longest FFD among major 35mm SLR mounts) |
| Inner Throat Diameter | 44.00 mm (1.732 in) |
| Bayonet Tabs | 3 locking tabs with counter-clockwise twist (opposite of Canon/Sony) |
| Historical Generations | Non-AI (1959) -> AI (1977) -> AI-S (1981) -> AF screw-drive (1986) -> AF-D (1992) -> AF-S Silent Wave (1998) -> AF-E Electronic diaphragm (2010s) |
| Aperture Control History | Spring-loaded mechanical stop-down lever (moved to electromagnetic diaphragm in 'E' lenses) |
| Camera Systems | Nikon F, F3, FM2, F5 (film), Nikon D850, D780, D6, D7500, D500 (digital DSLRs) |
60 Years of Mechanical Evolution
Nikon preserved backward lens compatibility for decades by layering electronic contacts and CPU chips around the mechanical 1959 bayonet. However, its narrow 44.0 mm throat diameter and long 46.5 mm FFD ultimately restricted ultra-fast optical apertures, prompting Nikon to transition to the wide $55\text{ mm}$ Z-mount for mirrorless.